In our recombinant screening program during the past year, we have picked up a very important recombinant. This recombinant mouse seems to have a crossing over within the H-2D region. The parental mice were of the H-2[unreadable]b[unreadable] and H-2[unreadable]d[unreadable] haplotypes. The recombinant has markers of D[unreadable]d[unreadable] and L[unreadable]b[unreadable] genes of the two parents. This suggests a gene order of D, L, R, and is the first such recombination in this region. In the past year, we produced several alloreactive clones that express Ia antigens. These clones grow without any external stimulation and have helped to solve the controversy that T cells do synthesize Ia antigens rather than taking them up from the macrophages. During the past year, we picked up five putative Ia mutants in our screening program and are analyzing them. We found that prolongation of allograft survival mediated by cyclosporin is not effective in certain MHC haplotypes, suggesting the in vivo metabolism of cyclosporin may be influenced by some MHC gene product. We are further analyzing this effect. We made considerable progress on the heterogeneity of Ia molecules. A few years ago we reported that there were more Ia polypeptides than were known at that time using monoclonal antibodies. Molecular biologists at that time claimed only isolation of four Ia genes, which made our results look doubtful. In the past six months, new Ia A[unreadable]beta[unreadable] and E[unreadable]beta[unreadable] genes have been identified, thus confirming our results on the biochemical identification of multiple Ia molecules. We are in the process of doing two-dimensional gel analysis and peptide mapping to confirm our results. (CS)